Field of the Invention
This invention relates to low pressure catalytic hydrocracking of refractory hydrocarbon charge stocks, such as, for example, a catalytic cracking cycle stock, a coker gas oil or shale oil, in a dual bed hydrotreating/hydrocracking cascade system.
Present refinery practice in upgrading coker gas oil generally involves hydroprocessing to remove hetero-atoms, followed by fluid catalytic cracking or high pressure hydrocracking in a two step operation. Such processes have entailed high equipment costs. Thus, fluid catalytic cracking of even hydroprocessed material requires high severity operation causing excessive coke formation, leading to reduced catalyst life. The necessity to use high pressure has placed an additional economic burden on the overall process.